How billet AR-15 receivers are made
SI Defense manufactures AR-15 lower and upper receivers that are machined out of solid aluminum billet blocks.

Two soon-to-be receivers being sprayed with coolant by the CNC machine
They have photos of the process and a video showing the CNC machine in operation. Very interesting.
Thanks to Health for the link.

I’d like to have one billet lower just because of the cool factor!
They should take full advantage of the billet 6061-T6 aluminum. It allows interesting designs to be produce.